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Plant Problems

By: Dr Gareth Evans - Updated: 16 Aug 2020 | comments*Discuss
Plants Pond Pests Problems Disease

A well planted pond makes a striking centre-piece in any garden. Although in general water plants tend to be less bothered by pests and disease than their dry-land counterparts, there are still a variety of problems which can affect them.

Keeping your aquatic plants in good health calls for a little vigilance. If you know the tell-tale signs to look out for – and act quickly – you should be able to make sure that your pond is always looking its best and stays an attractive garden feature.

Insect Pests

When it comes to pests, a very large proportion always seem to be insects – and the water garden is certainly no exception!

The 2.5cm (1 inch) long caterpillars of the China Mark Moth, for instance, emerge from eggs laid on the leaves of various kinds of water plants towards the end of the summer. These cream-coloured larvae, with their characteristic brown heads, bite oval-shaped holes in the foliage, fixing the pieces they remove together with silk to make a floating shelter where they feed on other aquatic plants, grow and ultimately pupate.

Although they are seldom a major problem, they can cause a fair bit of damage in small ponds – so, however fascinating you find their natural engineering skills, it’s best to remove any of their floating cases that you come across.

The Leaf-Miner Midge is another insect pest which, though not especially common, can be highly destructive to a wide range of water plants. The midge maggots themselves are small, thin and almost transparent, making them very difficult to see but, their presence is very easy to spot, especially if the attack is severe. Eating their way quickly through the soft tissues between the veins, the larvae rapidly produce skeletonised leaves in their wake.

There isn’t a treatment as such; all you can really do to improve things is pick off any affected leaves and destroy them.

Water Lilies

Of all pond plants, water lilies are probably the most commonly affected by pests and problems – some of which are entirely their own.

The Water Lily Beetle, for example, can cause major damage to their foliage, laying eggs that hatch into voracious black grubs with yellow undersides, which then eat their way through the leaves, causing big holes to appear. The damage they do eventually causes the leaf to shrivel and die, and if it is not removed, it will ultimately start to rot.

The only effective treatment is to ruthlessly remove and destroy the worst affected leaves and wash the remainder with a garden hose – and since this small brown beetle can lay three or even four clutches of eggs over the summer, you may have to do this more than once.

Fortunately this pest is only an occasional problem in small garden ponds, since it tends to prefer larger expanses of water, but if you are unlucky enough to find evidence of them, quick action will be necessary to save your plants.

Water Lily Aphids are another pest to be on the look-out for, especially during spells of hot, dry weather, when they may appear in huge numbers on the leaves, stems and buds. Although they are individually very small – much the same size as the more well-known vegetable black-fly – a large population feeding off your plants can cause weakened growth and distorted or absent flowers. Treatment again involves washing them off with a hose; they’ll make a tasty snack for any fish or wildlife in the pond.

Crown Rot

One of the most serious problems to affect water lilies, however, is not an insect, but a fungal disease related to potato blight – Water Lily Crown Rot – which can decimate a pond’s lilies if it is allowed to take hold. If you’re buying water lilies for your pond, it’s vital to inspect them carefully for any signs of infection, the easiest symptom to recognise being a black, soft spot on the lily’s rhizome.

The leaves of infected lilies will turn yellow and then break away from crown, which gradually blackens and eventually becomes foul-smelling; any affected plant needs to be removed and destroyed as soon as possible to contain the infection – which may spread to all of the lilies if left to run its course.

Fortunately, aquatic plants seem to be very resilient on the whole – which is a good job, given the obvious problems that trying to use any kind of pesticide in a pond would bring! Knowing what to look out for is half the battle and if you act swiftly to remove any affected foliage or plants as necessary, looking after your water garden shouldn’t give you too many problems.

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I had a thriving good sized garden pond filled with oxygenating plants, waterlilies and water hyacinth. I also have 3 golden orf and 3 shubunkins plus some black fish that appeared last year. There are dozens of great water snails too and I had to get rid of hundreds of leaves that were covered with their long jelly like egg cases or the population would have gone through the roof. Over the last 2 months i have lost the waterlily leaves completely and most of the oxygenating plants have gone. The only thing that is still thriving is the water hyacinth and the fish, and of course the snails. Are the snail the problem, or is it something else? Any advice would be welcome.
artyanne - 16-Aug-20 @ 10:52 AM
I created a garden pond, about two feet deep a couple of years ago. I added a small lily and an oxygenating plant. It has a small solar-powered fountain. This year, although the lily has thrown up over a dozen new pads, they only last a short time before turning yellow, then brown, and dis-attaching from the main plant. I notice everything in the pond is covered in a gelatinous slime, and the oxygenating plant is pretty much dead. All its foliage became separated from the base and floated up to the top. I would greatly appreciate any suggestions as to what is wrong, and what, if anything, I can do about it. Many thanks, John Moffatt
John - 26-Aug-19 @ 4:36 PM
We bought a miniature water lily 3 years ago and for the last two years it has had lovely small leaves and flowers on it. This year however it is huge! We only have a small pond so will have to get rid of it. Can anyone tell me why this would happen? I have had normal water lilies before and they don't start off small and get bigger, the leaves come out big to start with so I don't think it's this. Could it have reverte or something? Just curious if it couldhappen again if we buy another one.
Charlongo79 - 13-Aug-19 @ 4:32 PM
Our large pond is now almost over taken by water hawthorn how can it be controlled. As we are in advancing years who would you contact to help.
Dee - 1-Aug-19 @ 8:58 AM
Hey there, Saw this and that it was a fairly recent post so had to beg to ask.. I have FOUR nature ponds in my garden and they are all happy and healthy due to my diligence in keeping them all safe for wildlife and in the case of the largest pond, in the back, bottom-most part of our garden, water-life...in our case a HUGE tadpole population. Every year, for the third year now, I've added oxygen enhancing plants and, for my own enjoyment, a pink water lily. I'd love to have a pink lotus but the water lilies are less expensive and more accessible as a local garden centre stocks them in many varieties. I have tadpoles of every possible variety. Fat tails, long skinny tails, back feet first, front feet first. Not a single summer have they all survived, and not a single spring have I not met heartbreak as I scooped out many frogs that failed to survive our northeast Scottish winters. Yes,I follow the guidelines for spawn that go into hibernation over winter and have made certain the pond has been altered to be deep enough for frogs to survive under ice over winter. The back pond is the only pond on our property that has a frog and tadpole population. Last year, it was like New York City back there with spawn of all kinds. Some made it out over summer, some had to go under ice for winter. The water is crystal clear and tests as optimjal for amphibians and wildlife use (and our cats too who prefer ponds to the clean water in the house). ... HOWEVER This is now the third spring and going into summer that my water lilies seem to be some kind of addictive drug for tadpoles. I lost last year's lily and the one from the year before. I was told tadpoles shouldn't be a threat to water lilies but I now, at year 3, disagree. I planted a beautiful pink lily several weeks ago, it had one flower bud already on it and a well established plant. A week ago, a second bud began to rise to the water's surface as well as a new lily pad leaf. I was thrilled. But today...I had already noticed the tadpoles, like every year,k had been really happy to have the lily in the pond. This lily wants to be approximately 20 inches below surface, and it is. It gets lots of sunlight, has perfect water chemistry and gets water lily food every four weeks. It has no reason to fail. It's green, the flower buds are pink and ready to pop but it has magnetised the tadpoles like every lily before it. Tadpoles with fat tails, tadpoles with skinny tails...if they're tadpoles, they are on it. On the buds, on the pads, and on the stems. Tadpoles even in the stones that are on the uppermost layer of its basket. This morning, one lily pad has had a corner eaten away. It was not like this two days ago. I want to move it to the front of the garden to my ponds that have no tadpoles. They have had three resident frogs that sadly did not make it through winter (we had an extremely cold one and the ice was also very thick so I didn't think they'd survive especially given the p
Cari - 29-May-19 @ 6:08 PM
I have elephant ear plant but I have recently noticed the roots have white tentacle like things hanging off of them. Two of my koi carp have also died in the last week and one is looking ill. The water has also become strangely murky. Is this purely coincidental, or are these plants infected or something else.
Merar - 8-Jul-18 @ 8:55 AM
Dot - Your Question:
Tall reeds growing strongly in pond have what looks like blackfly. How can you treat please without damaging the fish?

Our Response:
It's probably best to take a picture of the pests and take it your garden centre for advice on which fish-friendly treatment to use.
PondExpert - 11-May-17 @ 2:08 PM
Tall reeds growing strongly in pond have what looks like blackfly. How can you treat please without damaging the fish?
Dot - 10-May-17 @ 12:01 PM
One of my goldfish appears to spend most of its time nose down but, if disturbed, is quite animated.Any comment would be most welcome.
Widower - 5-Jun-13 @ 9:22 AM
my waterlily has things that look like chunks of wet bread in it very often, n gets quite mucky looking frothy jellyish bubbles on the surface as well!! i have NO idea what this could be, n wonder if anyone has any ideas about what it is n how i can treat it??(preferably organically) please? n thanks in advance!!
retro-grrl - 13-Apr-13 @ 4:49 PM
My lilly pad leaves are being eaten. There are whitishjelly like lavae? about inch long on the underside of the leaves. some of the Lilly flowers are also being eaten. Anyone advise?
Todd - 13-Aug-12 @ 6:47 PM
Pond plant problems; I have water lily's with what looks like grains of pepper all over their leaves, top and bottom. It's not fungus, so it must be some kind of eggs? What do you suggest to get rid of these, without harmful insecticides?
Ang - 27-Jul-12 @ 8:17 PM
Dear Chef, the tubular jelly stuck under leaves is almost certainly pond snail eggs. I looked this up on Google last year when I had lots. Jennifer
Jennifer - 7-Jun-12 @ 2:47 PM
I am very curios as to what are the clear jelly like tubes 1 1/2 cm in length that are attached to plants and other fixed items in my pond. Are they the lava of leeches, snails or what? Also, I often find little white balls attached to weed, is this newt eggs? Can you help? Many Thanks Chef
Chef - 21-May-12 @ 8:11 PM
For the past several years my water lilies have given me a wonderful show , but this year although they have bloomed quiet well the pads are coming to the surface folded in half, also the blooms are not as large or as abundant as in the past, I would be most gratefull if you could offer any advice on my problems.
Michael Murphy - 2-Aug-11 @ 6:50 PM
We have a pond that we have pretty much left to nature, it's really a fish pond as it's around 3ft deep in the centre and doesnt have much in the way of marginal areas however it has lots of oxygenators in it and water hawthorn and was teaming with water boatman, greater diving beatles, shrimps, pond skators and water fleas etc. This year we decided to take some frogspawn from a friends pond as he has a carp that eats most of the spawn in his pond. The resulting tadpoles have done amazingly well and most have now turned into tiny frogs and are thriving. I have noticed however that i no longer see ANY water boatmen and diving beatles in the pond and in fact the only life i see apart from the tadpoles and frogs is snails, pond skators and the very occasional shrimp. I really don't understand what has happened to the beatles, i keep reading that the greater diving betales in both larva and adult form eat tadpoles and should be thriving in there so what is going on ? Any suggestions as to where all our beatles have gone would be very welcome. Ben
collbe - 17-Jun-11 @ 9:09 PM
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